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Responses Of Soil Respiration To Long-term Nitrogen And Phosphorus Additions Mediated By Plant Roots And Mycorrhizal Fungi In Subtropical Forests

Posted on:2022-12-09Degree:MasterType:Thesis
Country:ChinaCandidate:Y HongFull Text:PDF
GTID:2480306773487964Subject:Forestry
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Evergreen broad-leaf forest is a typical vegetation type in the subtropical region of China and is an important component of the global forest carbon sink.Soil respiration(Rs),as the second largest carbon flux in terrestrial ecosystems,has an important impact on forest carbon sinks.Currently,subtropical forests are facing the ongoing effects of increased nitrogen(N)deposition,and forests in the region are more susceptible to phosphorus(P)limitation than N.Whether increased N deposition will exacerbate soil P limitation in subtropical forests and thus affect Rs and its components(root,mycorrhizal fungi,microbial respiration),is not yet clear and greatly limits accurate assessment and prediction of future forest carbon sinks in the context of increased N deposition.Our study was carried out in a large platform of long-term N and P addition experiment(including 6 treatmments:control,low N,high N,P,low N+P and high N+P)in Zhejiang Tiantong Forest Ecosystem National Observation and Research Station,by long-term monitoring of Rs and differentiating components(with or without roots/mycorrhizal fungi),combined with soil,microbe and root indicators,to investigate dynamic change of Rs,as well as the effects and mechanisms of roots and mycorrhizal fungi on the response of Rs to long-term N and P addition in subtropical forests.The main results of this study are as follows.(1)By the analysis of Rs in 10 years,our results showed that there was a temporal effect on the response of Rs to N and P addition in subtropical forests:low N treatment significantly increased Rs at the beginning(+19.67%),P treatment increased Rs in 6th year(+29.91%),but all treatments showed a negative effect on Rs(24.93-47.50%reduction)in 10th year.The results indicated that Rs in subtropical forest was more influenced by enzyme activity and soil N content in early fertilization,while microbial community composition dominated the effect on Rs at later stage.(2)To address the negative effect of long-term N and P inputs on Rs,experiments differentiating components of Rs showed that plant roots and mycorrhizal fungi were to Rs in response to long-term N and P addition in subtropical forests,with presence of mycorrhizal fungi inhibiting Rs(-27.09%)without N or P addition,while root promoted Rs(+33.89%).After long-term N and P deposition,the mechanisms of Rsinhibited differed among treatments:when P input was more than N(P?low N+P),Rs was reduced due to the weakened contribution of roots(+12.14%?+17.87%);when N and P input was comparable or only low levels of N input(high N+P?low N),Rs was reduced due to the inhibited microbial respiration(-34.79%?-29.03%);and under high N treatment,Rs was inhibited due to the stronger negative effect of mycorrhizal fungi(-38.17%).Results of structural equation modeling indicated that long-term N and P addition indirectly regulate Rs of three components by affecting soil p H,enzyme activity,microbial biomass or microbial community composition.In summary,this study examines the response of Rs and its components to long-term N and P addition in subtropical forests and its mechanisms in the context of increased N deposition,revealing the temporal effects of Rs in response to N and P inputs:low N increased Rs initially,followed by P,but all treatments decreased Rsafter long-term fertilization.The experiment of differentiating components revealed the reasons for the inhibition of Rs:the shift from more P input to more N input,the inhibition of Rs in subtropical forest by treatments shift from a weakening of the contribution of plant roots to a reduction in microbial respiration and then to a more intense inhibition by mycorrhizal fungi.Long-term N and P input mainly regulated the changes of Rs of the three fractions indirectly by affecting soil properties and microbe.The study strengthen our understanding of soil carbon processes in response to increased N deposition in subtropical forests,and provide a basis for management of subtropical forest carbon sinks in the future.
Keywords/Search Tags:Nitrogen and phosphorus addition, Subtropical forest, Soil respiration, Mycorrhizal fungi, Plant roots
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